1. Field of the Invention
This invention relates to a surveying instrument for automatically tracking a target, such as a corner-cube reflector, and more particularly to the improvements in the surveying instrument for measuring a distance between the target and the instrument or an angle of a target-instrument line with a reference line.
2. Description of the Prior Art
Heretofore, a surveying method is known in order to search and determine a set out point with a surveying instrument for collimating a target such as a corner-cube reflector. As shown in FIG. 1, in the surveying method, a main body of the surveying instrument is located at a point P as a known point whereas the target is set at a point C in the vicinity of a set out point B as an unknown point. The set out point is defined as an unknown point of land corresponding to a point represented on a map. An operator stationed on the side of the main body collimates the target to determine the target point C. On the map, a positional difference between the points C and B is calculated with respect to the measured point C. For the calculation, the operator measures a distance .DELTA..alpha. in an X-axis direction and a distance .DELTA..beta. in a Y-axis direction in such a manner that the position of the set out point B is resolved into components of coordinates having an X axis (an optical axis 0 of a telescope mounted on the main body) and a Y axis (an axis perpendicular to the optical axis 0). The operator on the side of the main body informs an assistant on the side of the target about its result. The assistant with the target moves so that the difference between the target point and the set out point turns lessened. With the cooperation between the operator and assistant, the set out point is determined as a point of land corresponding to a point designated on the map.
In the conventional survey, at least two workers, one of whom is stationed on the side of the main body of the surveying instrument and the other on the side of the target, are needed.
It is preferable that the survey is carried out by only the worker stationed on the side of the target, in other words, to quit stationing an operator on the side of the main body for reducing the number of the workers.
To do so, it is needed to automatically inform the worker on the side of the target about whether the measurement of the target is completed or not. Such information is also needed in a case where more than two targets are used to measure distances or angles. That is, it is needed to automatically inform a plurality of workers with targets about whether the main body of the instrument is operating in a measuring mode in which the measurements of the respective targets are individually carried out. If the measuring mode is selected for one of the targets, it is impossible to track the other targets.